General The Higher Layer Protocol Data Unit field in the R-DATA Unit information elementisused to carry the Short Message Service (SMS) Cellular Messaging Teleservice (CMT)messages when the Higher Layer Protocol Identifier indicates Point-to-Point SMS. It should be noted that network support for CMT operation is beyond the scope of thisdocument and references to the Message Center are only provided to aid in describing thesupport of CMT operation over the air-interface.